Related Experiment Videos
Efficient incorporation of anti-HIV deoxynucleotides by recombinant yeast mitochondrial DNA polymerase
S Eriksson1, B Xu, D A Clayton
1Department of Developmental Biology, Stanford University School of Medicine, California 94305-5427, USA.
Abstract:
Saccharomyces cerevisiae mtDNA polymerase, isolated as a single 135-kDa recombinant polypeptide, showed high processivity and a capacity of use poly(dA).oligo(dT), poly(rA).oligo(dT), or primed bacteriophage M13 DNA as a template. In a primer extension assay, the enzyme exhibited an intrinsic 3'-5'-exonuclease activity. By optimizing the polymerization reaction conditions, apparent Km and Vmax values could be determined for the incorporation of dTTP, 2'-3'-dideoxy-TTP (ddTTP), 3'-azido-TTP (AZTTP), 3'-fluoro-TTP, dCTP, 2'-3'-dideoxy-CTP, and didehydro(d4)CTP. The yeast mtDNA polymerase used ddTTP, 3'-fluoro-TTP, and ddCTP almost as efficiently as natural deoxynucleoside trisphosphates. Both 3'AZTTP and d4CTP were each significantly less efficient as substrates. Overall, the kinetic data with mtDNA polymerase were very similar to those of the recombinant human immunodeficiency virus reverse transcriptase control. Terminally incorporated AZTTP or ddTTP was not removed by the 3'-5' exonuclease activity of mtDNA polymerase. This may explain the inhibition of mtDNA replication observed in anti-human immunodeficiency virus treatment with dideoxynucleoside analogs for their effects of mtDNA polymerase could be of value in future rational drug design.
Insights
Yeast mitochondrial DNA polymerase utilizes dideoxynucleoside analogs similarly to human immunodeficiency virus reverse transcriptase. This enzyme
Area of Science:
- Biochemistry
- Molecular Biology
- Yeast Genetics
Background:
- Mitochondrial DNA (mtDNA) replication is crucial for cellular energy production.
- Dideoxynucleoside analogs are used as antiviral drugs but can cause toxicity.
- Understanding mtDNA polymerase activity is key to developing safer antiviral therapies.
Purpose of the Study:
- To characterize the kinetic properties of Saccharomyces cerevisiae mtDNA polymerase.
- To investigate the enzyme's substrate specificity for natural and modified nucleoside triphosphates.
- To compare yeast mtDNA polymerase activity with human immunodeficiency virus reverse transcriptase.
Main Methods:
- Isolation and purification of recombinant yeast mtDNA polymerase.
- Primer extension assays to determine enzyme activity and processivity.
- Kinetic analysis (Km, Vmax) of nucleoside triphosphate incorporation.
- Assessing the 3'-5' exonuclease activity on terminally incorporated analogs.
Main Results:
- Yeast mtDNA polymerase demonstrated high processivity and utilized various DNA and RNA templates.
- The enzyme efficiently incorporated ddTTP and ddCTP, similar to natural deoxynucleosides.
- AZTTP and d4CTP were significantly less efficient substrates.
- Terminally incorporated AZTTP or ddTTP was resistant to the enzyme's exonuclease activity.
- Kinetic data closely resembled those of HIV reverse transcriptase.
Conclusions:
- Yeast mtDNA polymerase exhibits distinct substrate preferences for dideoxynucleoside analogs.
- The resistance of incorporated analogs to exonuclease activity may explain observed mtDNA replication inhibition.
- These findings offer insights for designing safer antiviral drugs targeting viral polymerases while sparing mtDNA polymerase.